Ignition diagnostics - symptoms of a bad condenser

[bkahler]

I'm helping someone trying to get a Cushman Truckster 3 cylinder engine to start and stay running. 

 

The symptoms are it will sometimes start and run for a few seconds and then it dies.  It will do this multiple times and eventually not fire at all.  You can go back and try again later in the day or the next day and the same thing happens.  Many other people have worked on it before it came to me trying to resolve this issue.  To the  best of my knowledge they all focused on the carburetor and fuel system.   I know for a fact that the fuel system is/was messed up.  It was supposed to have a bypass fuel filter that would bleed excess fuel back to the fuel tank, however the bypass filter was not installed until just recently.  The other issue was the original carburetor had two faulty solenoids and parts are no longer available so I replaced the carburetor yesterday with a new replacement.  The new replacement carburetor has been used in the same application before without issues.

 

 

Before trying to start the engine I also replaced the three spark plugs.  Here's a picture of what they looked like.  See any problems?

 

 

After installing the carburetor I tried starting it and it fired right off after a cranking for a bit.  It ran for about 10 seconds and died.  I restarted it and it fired right up and ran pretty good for about 10 seconds and died.  This repeated a couple of times but each time it ran for shorter periods and ran rougher.  Now it won't fire at all.  This sort of behavior is what others had reported as well with the original carburetor although they reported that it always ran really poorly. 

 

My gut feel is the condenser in the distributor is likely failing.  I'm not knowledgeable enough on what symptoms a bad/failing condenser can exhibit but I'm thinking as the condenser is getting hot it starts to fail and after it cools down it works for a bit until it gets hot again.  I'm going to try and start it again later this afternoon to see what happens. 

 

I guess the bottom line is, I think it's got an electrical problem of some kind. 

 

Thoughts?

 

 

[Los_Control]

What is really helpful is to have a spark plug tester

Just to check and see if you still has spark while it is dying then wont start.

Chances are if it has a good steady spark it may not be electrical .... I suspect you may be on the right track.

 

No idea about this engine, does it have a distributor? or are the points condenser behind the flywheel and have to remove it to get to them?

 

Either way, it might be a good idea to replace points and condenser and check the wiring closely.  Is there a pinched wire that might be grounding out or has poor insulation ...

 

Like our old distributors where the insulation fails and grounds out the points ... not necessarily bad points or condenser, but the wiring going to them.

I would just replace the points and condenser but mainly to inspect the wiring while there ... possibly remove the distributor if needed to really inspect it.

[bkahler]

Oddly enough I have an spark tester exactly like yours

 

I did test one spark plug before I wrote posted about it and I didn't see any spark.  I tried starting it a few minutes ago and no spark and it obviously didn't start.

 

Here's a little more background information.  The Cushman was purchased with out a distributor.  The correct distributor was sourced and new points, condenser, and cap were installed before the distributor was installed to the engine.  I'm going to start by pulling the distributor (it can only be fitted one way so it can't be 180 out) and looking things over inside and verifying all is correct. 

 

I find it odd that the previous owner had misplaced the distributor.  That kind of leads me to think there was some sort of electrical issue which is why the distributor was removed.  I'll let you know what I find.

[Sniper]

He condenser is not required for the ignition to work. It is there to help her then arcing across the points. You can remove for testing purposes

[bkahler]

1 minute ago, Sniper said:

He condenser is not required for the ignition to work. It is there to help her then arcing across the points. You can remove for testing purposes

 

Thanks for that little tidbit

 

[Los_Control]

12 minutes ago, bkahler said:

find it odd that the previous owner had misplaced the distributor.  That kind of leads me to think there was some sort of electrical issue which is why the distributor was removed. 

Most people do not remove the distributor for nothing ... sounds like you are on the right track.

 

I do not think there is a definitive test that follow steps one, two, three and if you get this result ... the condenser is bad.

Seems they can fail in such a way and the electricity just disappears into a black hole.

Sometimes they fail and when you test the spark it is unusually bright and that can mean it failed .... failed condenser is my go too, when I dunno.

[bkahler]

A number of years ago, the reproduction condensers for Triumph sports cars were all crap.  We all started hanging onto our 30 year old condensers and used them instead of new replacements.  I'll be digging into the ignition system tomorrow morning so stay tuned....

 

[oldodge41]

Possibly a coil issue. If it has one? I have seen coils fail with temperature rise.

[bkahler]

After cleaning a bunch of connectors, replacing the ignition switch, resetting the point gap (it was only a few thousands) and installing three new plugs the ignition system seems to be functional.  The condenser itself seems to check out but I will be replacing it in the near future, it is the original one as near as I can tell. 

 

The only issue now is it only runs on starter fluid.  The new carburetor does not seem to be carburating    That's next on the agenda to sort out.

 

Thanks!

 

[Ulu]

I once had the overdrive ignition circuit wire on my Edsel short to ground while driving. It blew the condenser wire right off the condenser. The engine stopped.

 

I taped up the shorted ignition wire, but that engine would not restart until I replaced the condenser.

 

I had a used one from our old Scout, at least 10 years old, which worked instantly.

 

I never bought a bad condenser for a car, but I bought computers loaded with faulty ones right from the factory.

 

20 years ago, Taiwan had a big run of bad motherboards. Not just one maker either. We had 8 at work which failed one by one, within a couple years.

 

Different boards with the same brand of weak capacitors, splitting open, & leaking burnt oil. 

 

 

[Los_Control]

I would replace the original working condenser and treat it like gold. If you suspect a bad condenser in the future, you can install the known good working condenser to verify.

My truck I have 4-5 working condensers around just because I do not trust them ... the originals I do trust.

 

I wonder what kind of fuel pump that has on it .... is the carburetor getting fuel to it? Cushman just sounds old ... wonder if the tank needs to come out to be cleaned    

[bkahler]

3 hours ago, Los_Control said:

I would replace the original working condenser and treat it like gold. If you suspect a bad condenser in the future, you can install the known good working condenser to verify.

My truck I have 4-5 working condensers around just because I do not trust them ... the originals I do trust.

 

I wonder what kind of fuel pump that has on it .... is the carburetor getting fuel to it? Cushman just sounds old ... wonder if the tank needs to come out to be cleaned    

 

That sounds like a good idea, once I can find a source for one that doesn't doesn't cost $35.  I'm tempted to use one from some other vehicle but I don't know if the capacitance is the same between vehicles.

 

I've believe I've eliminated any sort of electrical problem and same for fuel delivery.  All seems to be good there.  What I'm not seeing is much suction into the carburetor.  I'm going to check for compression and go from there.

 

[JBNeal]

On 2/27/2025 at 1:16 PM, bkahler said:

...Before trying to start the engine I also replaced the three spark plugs.  Here's a picture of what they looked like.  See any problems?

 

holey schmokes were either of these plugs correct?

[bkahler]

11 hours ago, JBNeal said:

holey schmokes were either of these plugs correct?

 

The two on the right are correct and likely the original plugs, because service bulletins eventually changed them to a BPR6EY.  The one on the left, who knows what went through the head of the guy who installed it, probably not much....